Most frogs lead a "biphasic" life: the first "tadpole" phase is aquatic and the second "adult" phase is terrestrial, says S. D. Biju of the University of Delhi, who also led the 2014 discovery of 14 new dancing frogs. But the Kallar dancing frog's tadpoles are "fossorial", meaning they always live under the soil.

"It is an interesting finding, predominantly because it was an entire family of frogs where we previously had very little indication of what the tadpoles were like," says amphibian biologist Jodi Rowley of the Australian Museum Research Institute, who was not involved in the study.

"Members of at least five other families are known to have fossorial tadpoles, so it's not unique among the frog world, but it is relatively rare," she adds.

"These tadpoles are also interesting because they are very similar to other fossorial tadpoles," says Rowley. "Clearly there's a particular body shape, etc. that works when you need to 'swim' underground."